$3 easy muffler end cap replacement

So the other day I was taking a nice morning ride on my booze-powered bicycle, and after all those times of me trying to get the end cap off the muffler manually, it came off by itself while I was on the road.  I stopped soon enough to go back and get it, but right as I got about 150 feet away a street sweeper just happened to come by and run over it!  Fortunately the end cap didn't get sucked up, but the cap was flatened and unusable.  I didn't want to ride without any back pressure for my engine so I had to peddle most of the way home.  The engine was also very loud without the cap.

I was frustrated because no matter how hot I made the cap with my torch, I couldn't bend it back to the right shape.  I thought I was going to need to make a new one and weld it on, but I found a solution that requires no welding and works just as well as the original!

The style of muffler I have is the one with the big baffle on the inside and a long tube protruding from the inside of the end cap.

Pretty much, the solution is to get a big steel washer and drill a hole through it.  Then bolt it on with a few smaller washers and a lock/spring washer.  And that's it!  Cost me $3 for the parts at Orchard Supply Hardware(my favorite hardware store).

Here are the parts I used:

• Fender washer - 1/2" x 2"
• Lock washer - 7/16"
• 2 flat washers - 7/16"
• 1 steel bolt - This can depend on your muffler so just pick the right one.

Any difference in performance?  Well since this homemade end cap doesn't have the baffle tube, the noise is just a tiny bit louder and I can see about 1mph better performance on hills!  Also sounds a little "throatier" than before!  If you lost your end cap and need a quick replacement, I'd say this is the way to go.  I've already road several miles with it and it stays on.

Iron pipe flange end cap

Murph on motorbicycling.com created a muffler end cap out of an "iron pipe flange" from the hardware store.  More of a makeshift replacement, really, but not bad!

Easy air filter

Who needs to fiddle with two screws every time just to get to the air filter?  This simple mod to the carburetor makes the size of the carb a bit smaller(for those who need frame clearance) and makes it easier to add/remove an air filter!  It looks like adb140275 from motorbicycling.com removed part of the air filter cover and zip-tied a piece of lawn mower air filter material around it.  To make this mod even easier, you can use a "quick release" zip tie so that you don't have to cut it every time you want to change it!

EDIT: I have a similar setup, but instead of the foam I use 3 layers of knee high stocking.  At Rite-Aid, you can get a pair for just a dollar.  Makes a nice high-flow filter if you're riding in an area without a lot of dirt!

NT carburetor walkthrough

While I'm modifying/cleaning my stock carburetor, I needed something to help me understand all the parts.  Norman on motorbicycling.com created an excellent thread on installing, disassembling, and rebuilding the stock NT carb!  It helped me a lot and newbs should read this(you're probably going to open up your carb at some point).

Carb cleaner can fuel tank

Made from an empty carb cleaner can, the top of a Coke bottle, and some JB Weld.  Not bad!

$10 homemade LED headlight

I've gone through 2 Bull(Bell) headlights and the large flashlight that I zip-tied to my handlebars slips around and isn't bright enough.  This seems like a great idea, and I think I'm going to do this! 

Soda bottle fuel tank adapter

So ya wanna use a soda bottle as a fuel tank?  Well now you can!


As if our bikes don't already attract enough attention.  Still, wacky fuel tanks FTW!  Not sure if a plastic bottle is the safest tank around but I still like the idea.

EDIT: I have read that gasoline sometimes melt the green plastic bottles, so be careful.

Ethanol bicycle update

After reading around on the internets, I became very tempted to see if it's possible to clean up our china girls with E85(ethanol) fuel!  Few people have accomplished this; in fact I could only find one person who claims to run their motorized bicycle on E85.  I featured his video in an earlier post, although the video bears little information and I could not get in contact with the guy.  Never the less, I set out to see if I could replicate his results.


Today I picked up a gallon of E85 from a Conserv Fuel station, and some ester-based synthetic oil(as apparently regular and petroleum-based synthetic separates from the ethanol).  After tweaking the carb needle and replacing the float bowl gasket(which was melted by the ethanol), I got my bike running on booze!  Since it was night time I didn't want to take the risk of having the engine seize in the middle of the road, so I rode around my neighborhood for about 3.5 miles.  Ran pretty good, too!  I may still have to enlarge the jet in the carb, but with the needle at the 3rd position and with the choke on just a little, it seems to run just fine!  Even pulled me up some steep hills!


We'll see how this goes.  Tomorrow I'm going to ride further and continue to test out the E85 as bike fuel.  If I continue to get good results, I might make a video about it with more details.  But don't be shocked if my engine blows up sometime this week!


Join the discussion on motorbicycling.com!

UPDATE 2: I drilled the main jet with a #60 drill bit, but this may have been a mistake.  The engine now runs way too rich even with the needle at it's leanest setting.  This means that the engine does almost nothing but 4-strokes and it bogs down and it won't make it up hills.  It actually ran better with the stock main jet and the choke about halfway up.  Still, I want to get the most power out of the ethanol fuel, so my next plan will be to get an iridium spark plug since I think the problem might be that the normal NGK plug doesn't have a good enough spark to ignite the higher amount of fuel being squirted into the cylinder.  If that doesn't work, I'll simply have to buy a new jet and start again.  =/ That is if I could find a hobby store that sells a #65 drill bit so I can solder and redrill, which would be way easier.


UPDATE 3: I soldered and redrilled my jet with a #67(approx) from a Dremel drill bit set.  I've now got the bike running on ethanol with the slide needle clip on the second position, which is considered default.  No need for the choke anymore.  I'll wait for the plug to run a while to see if it's running too lean or not, but if this works out, the only things that would need to be changed to convert a bike to ethanol would be the main jet and some new gaskets.  The NGK B6HS spark plug works fine.  Turns out I got some gunk inside the fuel intake(on the carb) and not enough fuel was getting to the engine.  I also tried a Briggs & Stanton spark plug and that works well with it too.  Perhaps better, but I'll have to do more testing.  My muffler came loose during my last test run, and that caused my idle to go out of control and I almost went on Mr. Toad's Wild Ride!  Good thing my clutch and kill switch were hooked up properly!  Plus my gas tank has been leaking again and I'm pretty close to chucking it in the garbage.  I can't be riding around with fuel dripping on to a hot engine.  I promise to post a video once I am done fixing those few things.

Clutch pucks from a car brake pad

Just another way to replace those old worn clutch pucks!  Metalliatic from motorbicycling.com discovered that using pieces of a car brake pad as clutch pucks works great!

Glade air-freshener muffler hack

This modification takes the end cap off the stock exhaust and replaces it with an empty Glade Air Freshener can and a hose clamp!  I don't know how junked stripped the paint off the can, but this sounds like an excellent idea!  Because it's adjustable, you could probably fine-tune your exhuast this way!

Homemade muffler clamp

Some people like to extend their exhaust using flexible tubing, and many of us don't like having the stock muffler hanging off those grade 5 studs!  This easy homemade setup is cheap and allows you to easily/firmly clamp your muffler to your frame!

Build your dream fuel tank with fiberglass!

You don't need expensive tools or metal-working skills to build your own custom fuel tank for your motorized bike!  If you're looking for an in-frame tank, or just something more sleek than the stock teardrop tank, fiberglass may just be the answer!


This instructables.com tutorial shows you how to make your very own fuel tank using fiberglass and fuel-safe epoxy resin!  The results look very professional, IMO.


What would make this project even cooler is if you could design your fuel tank as a computerized 3D model and paste together a prototype with Pepakura, and base your tank off that!

49cc engine running on E85 fuel

This guy claims to be able to run his 49cc bike engine on E85 fuel, which is 85% ethanol and 15% gasoline.  Many people think that ethanol can ruin your engine, so I don't recommend trying this just yet unless you have an extra china girl to spare.  Supposedly you have to use a larger jet in your carb, and the guy in the video says he added Marvel Mystery Oil to the fuel.  It's not clear what kind of 2-stroke oil he's using, since I believe the only oil that will dissolve in ethanol is pure ester-based synthetic 2-stroke oil.  Whether or not it's really currently possible, I'd love to be able to run my 66cc engine on mostly ethanol! 

Join the discussion on using ethanol with bike engines at motoredbikes.com!

Fuel fragrances for scented exhaust?

I came across this website the other day that sells "fuel fragrances" that are added to racing fuel to produce scented exhaust that help mask the nasty smell of burning fuel.  The scents you can buy include "Atomic Apple", "Burn Out Blueberry", "Rippin' Root Beer", and "Victory Vanilla"!  Though personally, I'd probably want to give my exhaust a minty smell, though it doesn't seem like they have that as an option.  Butterscotch would be pretty awesome too!

Some people find the idea of adding scent to your exhaust to be a "fruity" idea, but I think it's rather funny and I certainly wouldn't do it all the time.


But do these work with our little china girls?  I haven't tried it out, and I'm not sure anyone else has.  If you have any input, join the conversation at motorbicycling.com!

UPDATE: Pirate Cycles sells strawberry-scented oil that works in our 2-stroke engines!

"Velocity Stack" air filter mod

I don't think it's a true velocity stack, but it sure looks cool!  It's got to be better than the stock air filter/cover!  The fewer obstructions to the air intake, the better!  It can also be rotated to whatever angle you like, and I think this would go really well with the copper pasta tin fuel tank!

Modified KDX CDI

A normal CDI has a constant charging time, which means that it will run the engine but it will not lower its capacitance(charging time) to keep up with the speed of the engine.  This modified CDI setup allows for the capacitance to decrease when the RPM of the engine increases.  What does that mean?  Well it means faster uphill speed and an overall smoother ride!

DIY bike sidecar

This isn't specifically a motorized bicycle mod, but I think it's a worthwhile [and not often talked about] idea.  

This Instructables.com entry gives instructions to making your own bicycle sidecar!


I'm not sure how safe it would be to have another person in this car, but for areas with low traffic, it may not be a bad idea!  Even better, you could mount a cooler on the trailer and start your own mobile ice cream business!  What better way to pay off that 66cc engine than by using a little engineering to turn it into profit!


You may be wondering if this would legally disqualify your bike as a motorized bicycle: Well, this can depend on the laws in your area, but usually bikes with 3 wheels still qualify, which is what's excellent about this mod!  I'd love to see someone do this with a motorized bicycle!

Cheap homemade reed valve

For those of you who don't know what a reed valve is, I'll quote wikipedia:

Reed valves are commonly used in high-performance versions of the two-stroke engine, where they control the fuel-air mixture admitted to the cylinder. As the piston rises in the cylinder a vacuum is created in the crankcase beneath the piston. This vacuum opens the valve and admits the fuel-air mixture into the crankcase. As the piston descends, it raises the crankcase pressure causing the valve to close to retain the mixture and pressurize it for its eventual transfer through to the combustion chamber.

Pitchfork311 on motorbicycling.com took an $8 chainsaw reed valve and made it compatible with an HT engine! 

EDIT: Please, keep in mind that you must modify other parts of your engine(like trimming part of the piston skirt) before attempting anything like this.  Supposedly, you can't just slap a reed valve on a motor and call it done.

Read more about reed valves on bike engines!

Simple air cleaner mod promotes easier "breathing"

It's a similar idea to having a ram air system, only it involves simply shearing off a bit of the tubes off to allow air to more easily pass into the carb.  Neat and simple idea!

Homemade clutch lock

One of the most irritating aspect to building an MB is having things fall out due to vibration!  Fortunately, some parts, like the clutch lock, can be fabricated out of hardware store parts!